Increasing volume from 83mm pistons (1991cc) to 87mm (2188cc) will almost certainly need a different needle on the SUs.
I would start by trying to assess if you are indeed running weak (as I suspect) .
What do the plugs look like , are they blanched white, a sign of a weak mixture. Or you can use an analytical device, one of the popular ones was Gunson ColourPlug.
Once you have this I would start with the "normal" rich needle for these carbs which is the RH. Again run it up through the rev range to see where it is running well.
The Burlen website, that Peter has posted, has a lot of useful data, and most of the information is pretty clear and logical. If you follow this you won't go far wrong.
